Variations of shear-wave splitting parameters in the source region of the 2023 Türkiye doublet earthquakes

In this study,the shear-wave splitting parameters of local seismic events from the source regions of the 2023 Türkiye MW7.7 and MW7.6 doublet earthquakes(event 1 and event 2,respectively)were measured from June 1,2022,to April 25,2023,and their spatiotemporal characteristics were analyzed.The results revealed clear spatial and temporal differences.Spatially,the dominant fast-wave polarization direction at each station shows a strong correlation with the direction of the maximum horizontal principal compressive stress,as characterized by focal mechanism solutions of seismic events(MW≥3.5)near the station.The dominant fast-wave polarization direction and the regional stress field also showed a strong correlation with the intermovement of the Arabian Plate,African Plate,and Anatolian Block.Along the Nurdagi-Pazarcik fault zone,the seismic fault of event 1,stations closer to the middle of the fault where the mainshock occurred exhibited notably greater delay times than stations located towards the ends of the fault and far from the mainshock.In addition,the stations located to the east of the Nurdagi-Pazarcik fault and to the north of the Sürgüfault also exhibited large delay times.The spatial distribution of shear-wave splitting parameters obtained from each station indicates that the upper-crust anisotropy in the source area is mainly controlled by the regional stress field,which is closely related to the state of the block motion.During the seismogenic process of the MW7.7 earthquake,more stress accumulated in the middle of the Nurdagi-Pazarcik fault than at either end of the fault.Under the influence of the MW7.7 and MW7.6 events,the stress that accumulated during the seismogenic process of the earthquake doublet may have migrated towards some areas outside the aftershock intensive area after the earthquakes,and the crustal stress and its adjustment range near the outer stations increased significantly.With the exception of two stations with few effective events,all stations showed a consistent change in shear-wave splitting parameters over time.In particular,each station showed a decreasing trend in delay times after the doublet earthquakes,reflecting the obvious intensification of crustal stress adjustment in the seismogenic zone after the doublet earthquakes.With the occurrence of the earthquake doublet and a large number of aftershocks,the stress accumulated during the seismogenic process of the doublet earthquakes is gradually released,and then the adjustment range of crustal stress is also gradually reduced.

Study on cumulative effects of biological craniocerebral trauma under repeated blast

Repeated blast impacts on personnel in explosive environments can exacerbate craniocerebral trauma.Most existing studies focus on the injury effects of a single blast,lacking in-depth analysis on the injury effects and cumulative effects of repeated blasts.Therefore,rats were used as the experimental samples to suffer from explosion blasts with different peak air overpressures(167 kPa~482 kPa)and varying number of repeated blasts.The cumulative effect of craniocerebral trauma was most pronounced for moderate repeated blast,showing approximately 95%increase of trauma severity with penta blast,and an approximately 85%increase of trauma severity with penta minor blast.The cumulative effect of craniocerebral trauma from severe,repeated blast has a smaller rate of change compared to the other two conditions.The severity of trauma from penta blast increased by approximately 69%compared to a single blast.Comprehensive physiological,pathological and biochemical analysis show that the degree of neurological trauma caused by repeated blasts is higher than that of single blasts,and the pathological trauma to brain tissue is more extensive and severe.The trauma degree remains unchanged after double blast,increases by one grade after triple or quadruple blast,and increases by two grades after penta blast.

基于全球定位系统、第四纪断层滑动速率和横波分裂测量数据分析喜马拉雅东构造结岩石层垂直连贯变形

测量了喜马拉雅东构造结59个新的地震台站的SKS/SKKS波分裂参数,并结合前人在该区域得到的69个台站的横波分裂结果,以此来分析东构造结的地幔变形场特征。密集各向异性测量结果显示,快波方向在东构造结核心部位的南迦巴瓦为NE—SW方向,其周边地区为绕南迦巴瓦顺时针旋转的特征。我们基于全球定位系统(GPS)和第四纪断层滑动速率测量数据确定了一个连续的地表变形场,并以此来模拟每个台站预测的快波方向。通过快波方向的测量值和预测值对比分析,南迦巴瓦11个台站快波方向的测量值和预测值的平均角度差达60.8°,而其周边地区的角度差只有11.7°,这说明除南迦巴瓦以外,东构造结岩石层变形特征主要为垂直连贯变形模式,而南迦巴瓦不符合垂直连贯变形模式。地幔各向异性的复杂性和地表观察表明南迦巴瓦应变场的局部变形岩石层可能与印度板块在其下方俯冲作用有关。

Upper crustal velocity and seismogenic environment of the M7.0 Jiuzhaigou earthquake region in Sichuan, China

On August 8,2017,a magnitude 7.0 earthquake occurred in Jiuzhaigou County,Sichuan Province,China.The deep seismogenic environment and potential seismic risk in the eastern margin of Tibetan Plateau have once again attracted the close attention of seismologists and scholars at home and abroad.The post-earthquake scientific investigation could not identify noticeable surface rupture zones in the affected area;the complex tectonic background and the reason(s)for the frequent seismicity in the Jiuzhaigou earthquake region are unclear.In order to reveal the characteristics of the deep medium and the seismogenic environment of the M7.0 Jiuzhaigou earthquake region,and to interpret the tectonic background and genesis of the seismicity comprehensively,in this paper,we have reviewed all available observation data recorded by the regional digital seismic networks and large-scale,dense mobile seismic array(China Array)for the northern section of the North-South Seismic Belt around Jiuzhaigou earthquake region.Using double-difference seismic tomography method to invert the three-dimensional P-wave velocity structure characteristics of the upper crust around the Jiuzhaigou earthquake region,we have analyzed and discussed such scientific questions as the relationship between the velocity structure characteristics and seismicity in the Jiuzhaigou earthquake region,its deep tectonic environment,and the ongoing seismic risk in this region.We report that:the P-wave velocity structure of the upper crust around the Jiuzhaigoug earthquake region exhibits obvious lateral inhomogeneity;the distribution characteristics of the shallow P-wave velocity structure are closely related to surface geological structure and formation lithology;the M7.0 Jiuzhaigou earthquake sequence is closely related to the velocity structure of the upper crust;the mainshock of the M7.0 earthquake occurred in the upper crust;the inhomogeneous variation of the velocity structure of the Jiuzhaigou earthquake area and its surrounding medium appears to be the deep structural factor controlling the spatial distribution of the mainshock and its sequence.The 3D P-wave velocity structure also suggests that the crustal low-velocity layer of northeastern SGB(Songpan-GarzêBlock)stretches into MSM(Minshan Mountain),and migrates to the northeast,but the tendency to emerge as a shallow layer is impeded by the high-velocity zone of Nanping Nappe tectonics and the Bikou Block.Our results reveal an uneven distribution of high-and low-velocity structures around the Tazang segment of the East Kunlun fault zone.Given that the rupture caused by the Jiuzhaigou earthquake has enhanced the stress fields at both ends of the seismogenic fault,it is very important to stay vigilant to possible seismic hazards in the large seismic gap at the Maqu-Maqên segment of the East Kunlun fault zone.

Upper crustal anisotropy observed around the Longmenshan fault in the 2013 M_S7.0 Lushan earthquake region

Based on the shear wave splitting analysis of the seismic recordings at 17 temporary stations and three permanent stations, we measured the shear wave splitting parameters(i.e., the polarization direction of fast shear wave and the time delay of slow wave) to perform a systematic analysis of the crustal seismic anisotropy around the Longmenshan fault in the 2013 M7.0 Lushan earthquake region. We observed apparent spatio-temporal characteristics in the shear wave splitting parameters. The spatial distribution of fast polarization directions showed a clear partitioning in the characteristics from northwest to southeast in the focal region,which changed from NW-SE to NE-SW. In the northwest of the focal region, the fast polarization direction was oriented to NW-SE, which was parallel to the maximum horizontal compressive stress direction. However, the NE-SW fast polarization direction in the southeast of the focal region was parallel to the Longmenshan fault strike. For station BAX on the Central fault in the middle of the focal region, the distribution of fast polarization directions showed a bimodal pattern, with one dominant in the NE-SW direction and the other in the NW-SE direction. With regard to the temporal variation, the time delays were large in the initial stage after the mainshock but then gradually decreased over time and tended to be stable in the later period. This indicated that stress in the focal region increased to a maximum when the main shock occurred, with the stress release caused by the mainshock and aftershock activity, and the stress gradually decreased after a period of time. The scatter of fast polarization directions was large after the main shock, but over time the scatter gradually decreased, indicating that the Lushan earthquake caused a large perturbation in the local stress field. As the stress gradually decreased and was adjusted by the aftershock activity, the perturbation gradually weakened.

Multi-scale Analysis of the Relationships between Solar Activity, CO_(2) and Global Surface Temperature

To reveal whether the dynamics of solar activity precede those of global temperature, especially in terms of global warming, the relationship between total solar irradiance(TSI), which is treated as a proxy of solar activity, and global surface temperature(GST) is investigated in the frequency domain using wavelet coherence. The results suggest that the effect of TSI on GST is mainly reflected on the characteristic scale around 22 yr, and variations in TSI lead to changes in GST with some delay effect as shown by the phase difference arrows. However, this implicated relationship has been perturbed by excessive CO_(2) emissions since 1960. Through the combination of co-integration analysis and wavelet coherence, the hidden relationship between TSI and GST has been uncovered without the CO_(2) effect and the results further indicate that TSI has a positive effect on GST at the characteristic scale around 22 yr with a 3 yr lead.

Teleseismic shear wave splitting and intracontinental collision deformation of the northern Tibetan Plateau and the eastern Tarim basin

Shear wave splitting measurement of teleseismic data has been used to determine the fast polarization directions and delay times for 38 temporary stations and 15 permanent stations from a NW linear seismic array across the eastern Tarim basin(ETB) and the northern Tibetan Plateau(NTP),and 10 permanent stations on both sides of the array.We present an image of upper mantle anisotropy in the ETB and NTP using the 63 new measurements.The results show that the fast directions and delay times have complex spatial distribution characteristics.The delay times within the interior of the Tarim basin are very small,with an average value of 0.6 s,which is not only smaller than that in the Altyn Tagh fault and Tianshan on the southern and northern margins of the basin,but also smaller than that in the NTP,reflecting that the delay time of stable blocks is smaller than that of active blocks.Along the array,from east to west,the fast directions contrarotate from NNW in the southern Songpan-Garze terrane to NW in the northern Songpan-Garze terrane,to near E-W or ENE in the north of the East Kunlun fault and southern margin of the Qaidam basin,then first abruptly rotate to NW in the Qiman Tagh fault on the northwestern margin of the Qaidam basin,second abruptly rotate to ENE in the Altyn Tagh fault and south of the ETB,and third abruptly rotate to NW in the north of the ETB,then finally rotate to WNW in the Tianshan.The comparative analysis between the fast wave directions measured by shear wave splitting and predicted from the surface deformation field shows that,with the exclusion of the five observations with larger misfits within the interior of the ETB(with an average misfit of 27°),the misfits in the NTP and northern and southern margins of the Tarim basin are relatively small(with an average misfit of 9°).In addition,the fast wave directions of the tectonic units such as the Altyn Tagh fault,East Kunlun fault,and Tianshan are parallel to the strikes of faults and mountains in the region,which indicates that the deep and shallow deformations of the NTP and northern and southern margins of the ETB are consistent,where the crust-mantle coupling extent of lithospheric deformation is higher,according with the vertical coherent deformation of the lithosphere.Conversely,the crust-mantle coupling extent within the interior of the Tarim Basin is weak,and it is characterized by weak anisotropy,stable rigidity,and thick lithosphere,which may remain the “fossil” anisotropy of ancient craton.

Study of Impact Resistance Based on Porcupine Quills Bionic Thin-walled Structure

Using an electron microscope to observe the microstructure of a porcupine quills cross-section and a bionic method,a new bionic structure was proposed.The performance of the structure in terms of energy absorption,maximum impact force withstood,and impact force efficiency was evaluated using Ansys finite element simulation software to simulate the structure's impact.To examine the impact of ribs on the structural performance of the bionic porcupine quills,a control structure was developed.According to the results of the finite element simulation,the presence of ribs in the Bionic porcupine quills structure can transfer stress uniformly to the overall structure and share stress for some of the rupture-prone regions.Ribs reduce stress concentration in specific areas and increase the impact force efficiency of the structure.The SEA and IFE values of bionic porcupine quills were 30.01 kJ/kg and 84.22%,respectively.The structure is then optimized for parameter design in order to find the optimal structure by response surface in order to improve the structure's SEA and decrease its MIF.In order to evaluate the precision of the response surface,the optimal structure predicted is validated using finite element simulation.

A diagnostic prediction model for hypertension in Han and Yugur population from the China National Health Survey (CNHS)

Background:The prevalence of hypertension is high among Chinese adults,thus,identifying non-hypertensive individuals at high risk for intervention will help to improve the efficiency of primary prevention strategies.Methods:The cross-sectional data on 9699 participants aged 20 to 80 years were collected from the China National Health Survey in Gansu and Hebei provinces in 2016 to 2017,and they were nonrandomly split into the training set and validation set based on location.Multivariable logistic regression analysis was performed to develop the diagnostic prediction model,which was presented as a nomogram and a website with risk classification.Predictive performances of the model were evaluated using discrimination and calibration,and were further compared with a previously published model.Decision curve analysis was used to calculate the standardized net benefit for assessing the clinical usefulness of the model.Results:The Lasso regression analysis identified the significant predictors of hypertension in the training set,and a diagnostic model was developed using logistic regression.A nomogram with risk classification was constructed to visualize the model,and a website(https://chris-yu.shinyapps.io/hypertension_risk_prediction/)was developed to calculate the exact probabilities of hypertension.The model showed good discrimination and calibration,with the C-index of 0.789(95%confidence interval[CI]:0.768,0.810)through internal validation and 0.829(95%CI:0.816,0.842)through external validation.Decision curve analysis demonstrated that the model was clinically useful.The model had a higher area under receiver operating characteristic curves in training and validation sets compared with a previously published diagnostic model based on Northern China population.Conclusion:This study developed and validated a diagnostic model for hypertension prediction in Gansu Province.A nomogram and a website were developed to make the model conveniently used to facilitate the individualized prediction of hypertension in the general population of Han and Yugur.